Abstract: We present a theoretical study on optical properties such as optical conductance and light transmission coefficient for mono- and multi-layer graphene systems with AB- and ABC-stacking. Considering an air/graphene/dielectric-water structure, the optical coefficients for those graphene systems are examined and compared. The universal optical conductance sigma(N)(0)=N pi e(2)/(2h) for N layer graphene systems in the visible region is verified. For N 3 layer graphene, the mini-gap induced absorption edges can be observed in odd layers AB-stacked multilayer graphene, where the number and position of the absorption edges are decided by the layers number N. Meanwhile, we can observe the optical absorption windows for those graphene systems in the infrared to terahertz bandwidth (0.2-150 THz). The absorption window is induced by different transition energies required for inter- and intra-band optical absorption channels. We find that the depth and width of the absorption window can be tuned not only via varying temperature and electron density but also by changing the number of graphene layers and the stacking order. These theoretical findings demonstrate that mono- and multi-layer graphene systems can be applied as frequency tunable optoelectronic devices working in infrared to terahertz bandwidth. (C) 2014 Elsevier B.V. All rights reserved.

Abstract: Methane reforming by plasma catalysis is a complex process that is far from understood. It requires a multidisciplinary approach which ideally takes into account all effects from the plasma on the catalyst, and vice versa. In this contribution, we focus on the interactions of CHx (x = {1,2,3}) radicals that are created in the plasma with several nickel catalyst surfaces. To this end, we perform reactive molecular dynamics simulations, based on the ReaxFF potential, in a wide temperature range of 4001600 K. First, we focus on the H2 formation as a function of temperature and surface structure. We observe that substantial H2 formation is obtained at 1400 K and above, while the role of the surface structure seems limited. Indeed, in the initial stage, the type of nickel surface influences the CH bond breaking efficiency of adsorbed radicals; however, the continuous carbon diffusion into the surface gradually diminishes the surface crystallinity and therefore reduces the effect of surface structure on the H2 formation probability. Furthermore, we have also investigated to what extent the species adsorbed on the catalyst surface can participate in surface reactions more in general, for the various surface structures and as a function of temperature. These results are part of the ongoing research on the methane reforming by plasma catalysis, a highly interesting yet complex alternative to conventional reforming processes.

Abstract: The effects due to intersubband coupling and screening on the ionized impurity scattering are studied for a quasi-two-dimensional electron system in delta-doped semiconductors. We found that intersubband coupling plays an essential role in describing the screening properties and the effect of ionized impurity scattering on the mobility in a multisubband system. At the onset of the occupation of a higher subband, the screening due to the intersubband coupling leads to a reduction of the small angle scattering rate in the lower subband. We showed that such an effect is significant in a delta-doped quantum well and results in a pronounced increase of the quantum mobility at the onset of the occupation of a higher subband. (C) 1996 American Institute of Physics.

Abstract: Ion irradiation of carbon nanotubes very often leads to defect formation. However, we have recently shown that Ar ion irradiation in a limited energy window of 1025 eV may enhance the initial cap nucleation process, when the carbon network is in contact with the metal nanocatalyst. Here, we employ reactive molecular dynamics simulations to demonstrate that ion irradiation in a higher energy window of 1035 eV may also heal network defects after the nucleation stage through a non-metal-mediated mechanism, when the carbon network is no longer in contact with the metal nanocatalyst. The results demonstrate the possibility of beneficially utilizing ions in e.g. plasma-enhanced chemical vapour deposition of carbon nanotubes.

Abstract: YBa(2)Cu(3)O(7-delta) (YBCO) grain boundaries characterized by a misalignment of the c-axes (45 degrees c-axis tilt or 45 degrees c-axis twist) have been obtained by employing a recently implemented biepitaxial technique. Junctions based on these grain boundaries exhibit good Josephson properties useful for applications. High values of the I(C)R(N) product and a Fraunhofer-like dependence of the critical current on the magnetic field, differently from traditional biepitaxial junctions, have been obtained. The correlation between transport properties and microstructure has been investigated by Transmission Electron Microscopy (TEM), which was also performed on previously measured junctions. The presence of atomically clean basal plane (BP) faced tilt boundaries, among other types of interfaces, has been shown. The possibility of selecting these kinds of boundaries by controlling film growth, and their possible advantages in terms of reproducibility and uniformity of the junction properties an discussed. The possibility of employing these junctions to explore the symmetry of the order parameter is also discussed. (C) 1999 Elsevier Science B.V. All rights reserved.